The present invention is related to transient voltage suppression, and in particular to a circuit topology for providing transient voltage suppression.
Transient voltage suppression is employed to prevent temporary spikes in voltage from damaging loads, such as power supplies. Various circuit topologies have been devised to provide the desired voltage suppression. For instance, in one topology a transient voltage suppression device clamps the input voltage range of the power supply to a level within the rating of the power supply. However, if the voltage suppression device fails to activate, then the load or power supply will be unprotected from transient voltage surges.
In another topology, a field effect transistor (FET) is provided in series with the input line providing power to the load (i.e., the high-side of the load, as opposed to the return line or low-side of the load). During a detected transient voltage surge, the FET is turned OFF to cause the transient voltage to be developed across the series FET. Either N-channel or P-channel FETs may be used. The drawback of an N-channel FET is that the gate voltage must be higher than the input line voltage provided at the drain of the FET. As a result, an artificially high gate voltage (i.e., voltage higher than the output voltage being supplied by the power supply) is required to operate the FET in the ON position. Typically, a charge pump and/or transformer is used to generate the gate voltage for the FET, but the conversion to alternating current for transformer operation and/or rapid switching for charge pump operation tends to generate undesirable radio frequency emissions.
Alternatively, the N-channel FET may be replaced with a P-channel FET. However, the P-channel FET is limited to circuits with relatively small power needs because of the relatively high ON resistance and associated power dissipation generated by the P-channel FET while operating in the normal ON state.